feat: OpenRC and runit init backends behind an Init interface

Extract init-neutral unit resolution into service/, add initsys.Init with systemd, openrc and runit backends, selected by 'init:' config or autodetect. OpenRC and runit are root only; rootless units run as system services as that user. Add docs and generated examples for all three.

cmd/startall.go

@@ -6,7 +6,7 @@ import (
 
 	"github.com/spf13/cobra"
 	"github.com/warkanum/unitdore/config"
-	"github.com/warkanum/unitdore/systemd"
+	"github.com/warkanum/unitdore/initsys"
 )
 
 var startallCmd = &cobra.Command{
@@ -28,6 +28,10 @@ func runStartall(cmd *cobra.Command, args []string) error {
 	}
 
 	prefix, suffix := cfg.Prefix, cfg.Suffix
+	ini, err := initsys.New(cfg)
+	if err != nil {
+		return err
+	}
 
 	units := make([]config.Unit, len(cfg.Units))
 	copy(units, cfg.Units)
@@ -45,12 +49,12 @@ func runStartall(cmd *cobra.Command, args []string) error {
 		if !u.Enabled {
 			continue
 		}
-		if !systemd.IsInstalled(u, prefix, suffix) {
+		if !ini.IsInstalled(u, prefix, suffix) {
 			fmt.Printf("  ! %s: not installed — run 'unitdore install' first\n", u.Name)
 			continue
 		}
-		fmt.Printf("  ▶ starting: %s...\n", systemd.ServiceName(u, prefix, suffix))
-		if err := systemd.Start(u, prefix, suffix); err != nil {
+		fmt.Printf("  ▶ starting: %s...\n", ini.ServiceName(u, prefix, suffix))
+		if err := ini.Start(u, prefix, suffix); err != nil {
 			fmt.Printf("  ✗ failed: %s: %v\n", u.Name, err)
 			failed++
 		} else {